1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to a data transmission/reception method and system for removing cell interference between neighbor cells in a communication system having a multi-cell structure.
2. Description of the Related Art
In the next generation communication system, active research is being conducted to provide high-speed services having various Qualities of Service (QoS) to users. Particularly, a study is being conducted to support high-speed services that can guarantee mobility and QoS for a Broadband Wireless Access (BWA) communication system such as a Wireless Local Area Network (WLAN) system and a Wireless Metropolitan Area Network (WMAN). An Institute of Electrical and Electronics Engineers (IEEE) 802.16a/d communication system and an IEEE 802.16e communication system are typical BWA communication systems.
The IEEE 802.16a/d communication system and the IEEE 802.16e communication systems employ Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) to support a broadband transmission network for physical channels of the WMAN system. The IEEE 802.16a/d communication system currently considers only the state in which a Subscriber Station (SS) is fixed, i.e. the state in which mobility of the SS is never considered, and the single-cell structure. Unlike the IEEE 802.16a/d communication system, the IEEE 802.16e communication system considers mobility of the SS in the IEEE 802.16a communication system, and an SS having the mobility will herein be referred to as a Mobile Station (MS).
In the BWA communication system, because the limited resources, i.e. frequency, code and time slot resources, are shared by a plurality of cells constituting the communication system, interference may occur between the plurality of cells, especially between neighbor cells. The interference between neighbor cells is considerable in a communication system using a frequency reuse factor of 1. More specifically, the use of the frequency reuse factor of 1 increases efficient utilization of the frequency resources, but an MS located in the cell boundary between neighbor cells suffers a considerable decrease in a Carrier-to-Interference and Noise Ratio (CINR) of a signal received from a serving Base Station (BS) that manages the cell where the MS is located. That is, in the communication system using the frequency reuse factor of 1, an MS located in the vicinity of the serving BS may have no difficulty in communicating with the serving BS due to the low interference, but the MS located in the cell boundary suffers interference from a neighbor BS that manages a neighbor cell, decreasing the system performance.
In order to remove the interference between neighbor cells, the MS improves a received CINR from the serving BS using an interference remover in a downlink interval, and the serving BS improves a received CINR from the MS using an interference remover in an uplink interval, thereby improving the system performance. However, the scheme of improving the system performance using the interference remover cannot realize significant improvement of the system performance, because the interference canceller may not accurately cancel the interference signals or may not correctly restore the signals received from the serving BS.
FIG. 1 illustrates a configuration of a conventional BWA communication system.
Referring to FIG. 1, the BWA communication system has a multi-cell structure, i.e. has a cell1 110 and a cell2 120, and includes a BS1 111 and a BS2 121 that manage the cells 110 and 120, respectively, and an MS 113 that is located in cell1 110 and receives a communication service from BS1 111. For convenience, signal exchanges between the BSs 111 and 121 and the MS 113 are assumed to be performed through a first channel h1 and a second channel h2, respectively, using OFDM/OFDMA.
The MS 113 is located in the boundary of cell1 110, and BS1 111 transmits data to MS 113 located in cell 110 through a frequency region (A-1) 151. The BS2 121 that manages cell2 120, which is a neighbor cell of MS 113, transmits data to MSs located in cell2 120 through a frequency region (B-1) 161 and a frequency region (B-2) 163. In this case, the MS 113 located in the boundary of cell1 110 can receive the interference caused by the data transmitted by BS2 121, which is a neighbor BS, while receiving data from BS1 111, which is the serving BS, through frequency region (A-1) 151.
In other words, there is an overlapping region where frequency region (A-1) 151 allocated to MS 113 by BS1 111 and frequency regions (B-1) 161 and (B-2) 163 allocated to the MSs located in cell2 120 by BS2 121 overlap each other. The overlapping region is an interference region for MS 113 located in the boundary of cell1 110. Because of the presence of the interference region, if BS2 121 of cell2 120 transmits data through frequency regions (B-1) 161 and (B-2) 163 using the same time-frequency resources as those of BS1 111 while MS 113 is receiving data from BS1 111 through frequency region (A-1) 151, MS 113 located in the boundary of cell1 110 decreases in the received CINR, causing a decrease in reception performance of the MS 113.
In order to prevent the decrease in the CINR due to the interference of cell2 120, MS 113 removes the interference using the interference remover as described above. However, because BS1 111 and BS2 121 allocate resources independently of each other, the interference remover may not accurately remove the interference signals or may not correctly restore the signals received from the serving BS1 111. Therefore, it is difficult to expect noticeable improvement of the system performance.
More specifically, if BS2 121 of cell2 120 transmits data through frequency regions (B-1) 161 and (B-2) 163 while MS 113 is receiving data from BS1 111, or a serving BS, through frequency region (A-1) 151, the data transmitted by BS2 121 serves as interference to MS 113. In order to remove the interference, MS 113 should have information on the overlapping region between frequency region (A-1) 151, and frequency regions (B-1) 161 and (B-2) 163, i.e. information on the interference region. In addition, MS 113 should have information on a Modulation and Coding Scheme (MCS) level of the data transmitted through frequency region (B-1) 161 and an MCS level of the data transmitted through frequency region (B-2) 163, and should also have information on channel h2 of cell2 120.
That is, in order to remove the inter-cell interference of cell2 120, the MS 113 should estimate the channel of cell2 120 using a pilot received from BS2 121. The need for the information by MS 113 for the inter-cell interference removal acts as a heavy load to MS 113, decreasing the system performance. When the MS 113 has a plurality of neighbor cells, the decrease in the system performance can be more considerable.